Anisotropic arc-spark emission electrodes



April 1966 L. J. GARBINI ETAL 3,248,592

ANISOTROPIC ARC-SPARK EMISSION ELECTRODES Filed Sept. 10, 1963 l6 A W/ 22 24 AB |7- PLANEs PLANES PLANES AXIS 7 00" AB A 0242" c PLANES PRIOR AB PLANEs ART PL ENEs HQ 6 J FIG. 5

c AB AXIS PLANES l llllll PYRO PYRO- PYRO- $3 ATP. GPA EEK'SH GRA L TH A MENT LENGTH ITE TE TE TE TE c- AB- c- AB- AXIS PLANE AXIS PLANE Co 3453.3 8.2 2.60 9.53 2400 52 e9 75 Y 3242.| L37 L34 ||.5 3070 37 49 8| Pb 2833.l 298 L60 MB 4300 25 7 9s RELATIVE INTENSITIES FROM 4500 20 5 a2 '2 3 BACKGROUND COMPARISON INVENTORS LEO J. GARBINI JOHN B. MOONEY CARL E. SCHODER RNEY United States Patent Ofiice 3,248,592 Patented Apr. 26 1966 3,248,592 ANISOTROPIC ARC-SPARK EMISSIQN ELECTRQDES Leo J. Garbini, Sunnyvale, John B. Mooney, Saratoga,

and Carl E. Schoder, Los Altos, Calif, assignors to Varian Associates, Palo Alto, Calif., a corporation of California Filed Sept. 10,1963, Ser. No. 307,990 19 Claims. (Cl. 313-355) This invention relates in general to arc-spark electrodes and more particularly to anisotropic arc-spark emission spectroscopy electrodes and anisotropic illumination electrodes.

Qualitative and quantitative analysis by spectroscopic or spectrochemical techniques has become an extremely important analytical tool in practically speaking all of the scientific disciplines dealing with matter and its properties. Regardless of which analytical method is employed, qualitative or quantitative, and regardless which of the various specific techniques such as visual photographic, with or without internal standards, etc., is used by the analyst, the characteristics of the electrodes employed to generate the are are of paramount importance in achieving meaningful and accurate results.

The physical characteristics of the electrodes, both sample and counter are important contributors in determining the properties of the arc produced. Naturally, materials having extremely high melting points and a high degree of purity are used in emission spectoscopy. One of the most widely used materials possessing the above characteristics is graphite. Ordinary or commercial graphite is isotropic that is, it has a random orientation of its crystals. Thus the electrical and thermal properties of graphite are uniform in all dimensions. Therefore, ordinary graphite electrodes employed in emission spectroscopy work will conduct heat as easily along the surface from which an arc is being drawn as well as perpendicular thereto. This results in inefiiciency due to uneven burning of the electrodes. Furthermore, arcs produced from ordinary isotropic graphite have a tendency to wander or drift about the electrode surface and this is highly undesirable since it results in nonuniform volatilization and/ or excitation of the specimen under analysis. Furthermore, hot spots develop on the electrodes due to uneven burning and cause either electron or ion bombardment of the electrode which will burn off electrodes unevenly and result in uneven-rates of volatilization of different areas of the sample or specimen which results in questionable validity of multiple studies of a given specimen.

Arc-spark electrodes for illumination applications such as for search lights, motion-picture projectors, etc., are enhanced by utilization of stable sources and such sources have heretofore not been as stable as desired.

The present invention through the utilization of anisotropic electrodes enhances the stability of the source for such illumination applications.

The present invention obviates the above deficiencies in prior art emission spectroscopic electrodes through the utilization of novel electrodes comprising anisotropic physical parameters so oriented with respect to the arc, of the specimen under consideration such that increased spectral sensitivity, more uniform burning of the arc and electrodes, and enhanced arc stability are achieved thereby individually or collectively, depending on the particular electrode from and orientation chosen. The present invention, through the use of anisotropic pyrolytic graphite emission spectroscopic electrodes having the C-axis and A-B planes thereof oriented in a predetermined manner with respect to the central axis of the are drawn between the electrodes, results in heretofore unattainable arc characteristics with resultant enhanced emission spectroscopic properties. The present invention further provides a variety of electrode configurations having novel characteristics by virtue of the anisotropic characteristics and preselected orientation of the C-axis and AB planes of the electrode material. Pyrolytic graphite is herein defined as that form of vapor deposited carbon which is frequently referred to as anisotropic pyrolytic graphite. The A-B planes of pyrolytic graphite are characterized by having properties similar to a conductor whereas the C- axis is characterized by having properties similar to an insulator. Therefore, as will be explained in more detail hereinafter, the electrical and thermal conductivity in the A-B planes is much greater than along the C-axis. Hereinafter, AB plane signifies the plane of high thermal and electrical conductivity of an anisotropic material such as pyrolytic graphite while C-axis signifies the axis of an anisotropic material such as pyrolytic graphite which has low electrical and thermal conductivity in relation to the AB plane.

A principal object of the present invention is the provision of improved emission spectroscopic electrodes.

A feature of the present invention is the provision of emission spectroscopic electrodes having anisotropic physical parameters.

Another feature of the present invention is the provision of emission spectroscopic electrodes formed from pyrolytic graphite.

Still another feature of the present invention is the provision of various electrode configurations formed from an anisotropic material wherein the C-axis and A-B plane of the material are selectively preoriented in order to obtain desired characteristics for an are drawn from or drawn to said electrode or between electrode pairs.

These and other features and advantages of the present invention will be more apparent upon a perusual of the following specification taken in conjunction with the accompanying drawings wherein,

FIG. 1 is a sectional view of 'a pair of electrodes having anisotropic arcing surfaces wherein the A-B planes of the materials forming the arcing surfaces are disposed normal to the central axis of the arc to be drawn between said electrodes.

FIG. 2 is a sectional view of a pair of electrodes having anisotropic arcing surfaces, wherein the A-B planes of the material forming the arcing surfaces are disposed parallel to the central axis of the arc to be drawn between said electrodes.

FIG. 3 is a sectional view of typical prior art electrodes formed from isotropic graphite.

FIG. 4 is a sectional view of a pair of electrodes having a typical prior art configuration as shown in FIG. 3 and having a base or substrate of conventional isotropic material, wherein an anisotropic material is deposited thereon to form the arcing surface such that the A-B planes of the deposited material parallel the particular surface configuration of the base or substrate.

FIG. 5 is a section view of a pyroformed anisotropic cup shaped electrode supported by a base of conventional material.

FIG. 6 is a sectional view of a boiler type pair of electrodes, wherein the boiler cap is formed from a pyroformed anisotropic material.

FIG. 7 is a sectional view of another boiler type pair of electrodes, wherein the boiler cap is formed from an anisotropic material.

, FIG. 8 is a sectional view of a pair of conventional isotropic electrodes, wherein the electrode has a central arcing post and wherein the opposing surfaces of both of said electrodes are formed from an anisotropic material.

FIG. 9 depicts achart comparing the relative spectral sensitivities for dimensionally equivalent electrodes conforming to FIGS. l3 for afew specimen elements using Li CO as a matrix.

FIG. 10 depicts a chart comparing the percent transmission at different wavelengths of ordinary or non-coherent light through film previously exposed to arcs using electrodes conforming to FIGS. 1-3.

Directing our attention now to FIG. 1, there is depicted a pair 11 of electrodes wherein the sample electrode 12 has a base or substrate 13 material which is preferably of isotropic graphite. Isotropic is used to define a material having for all practical purposes, uniform physical characteristics in every direction. Mounted on base 13 is a cup shaped tip of an anisotropic material, preferably pyrolytic graphite, wherein the AB planes of the polycrystalline material are disposed parallel to the counter electrode 14, or expressed another way, normal to the central axis of an are drawn between electrodes 12 and 15. The C-axis of the tip material is aligned with the central axis of an are drawn between the electrodes. The counter electrode 15 has a conventional base '16 of graphite or any other suitable material and a cone shaped tip portion 17 of an anisotropic material preferably identical to the cup shaped tip 14. The AB planes of the polycrystalline tip of counter electrode 15 are oriented in the same manner as the cup shaped tip electrode 14.

The properties of anisotropic pyrolytic graphite are such that the individual crystals are highly oriented as opposed to the random orientation between individual crystals of ordinary or commercial graphite. Pyrolytic graphite is at present manufactured by vapor deposition of carbon from an organic vapor state onto a substrate which is maintained at elevated temperatures such as for example, 2100 C under pressures of around 10 cm. Hg. Methane is a suitable gas for producing pyrolytic graphite. The orientation of the individual crystals deposited on the substrate is such that the planes of deposition (parallel to the deposition substrate) hereinafter and previously referred to as AB planes, have different physical and electrical properties than the axis normal to these planes, hereinafter and previously referred to as the C-axis. For example, it has been determined that thermal conductivity in the AB plane is around 200 times greater than along the C-axis. The electrical characteristics of pyrolytic graphite exhibit similar directionality. For example, very low electrical resistivity, such as 4 1O ohm-cm. at room temperature occurs along the AB planes. Thus it might be said that pyrolytic graphite behaves like an insulator along the C-axis and like a conduct-or in the AB plane. is said to be anisotropic.

The above mentioned characteristics are advantageously utilized in the electrode configuration depicted in FIG. 1 as follows:

Since the AB plane exhibits high uniform thermal conductivity, it will conduct heat rapidly and uniformly across the entire arcing surface to produce an extremely stable arc. Furthermore, since thermal conductivity along the C-axis is negligible in comparison to thermal conductivity in the AB planes, heat will tend to concentrate at the arcing surface rather than diffusing down or up, as the case may be, into the region of and into the base or substrate. Therefore, the present invention depicted in FIG. 1 achieves higher electrode temperatures for a given voltage and current in comparison to ordinary isotropic graphite electrodes 18 and 19 having equivalent physical parameters as depicted in prior art FIG. 3. This is particularly useful if fast volatilization and/or excitation of the specimen is desired.

FIG. 2 depicts a similar electrode configuration as shown in FIGS. 1 and 3 with the exception that in this case, the tip portion 20, 2-1 of electrodes 22 and 23 have the C-axis disposed parallel to and forms the arcing surface while the AB planes are paralleled with the central Therefore, pyrolytic graphite arc axis. The benefits to be derived from this orientation are a lower average surface temperature for a given energy input which provides reduced background or white radiation and thus enhances spectral sensitivity.

FIG. 4 depicts a pair of isotropic electrodes 24, 25 with base or substate portions 26, 27 having an isotropic coatings 28, 29 deposited thereon. Pyrolytic graphite is formed by vapor deposition of an organic vapor on a substrate and the AB planes will be paralleled with the substrate surface upon which the pyrolytic graphite is deposited while the C-axis will accordingly be normal thereto. This technique is advantageously employed to form the coatings depicted in FIG. 4. All the advantages derived from having the AB planes form the arcing surface as described in connection with FIG. 1 are present in the embodiment of FIG. 4. Furthermore, even more rapid heat up times to peak are operating temperature are achieved with the coated version since heat can flow uniformly along the internal portions of the cup without encountering any C-axis thermal resistance.

FIG. 5 depicts a pyr-oformed anisotropic cup electrode 30 mounted on a base 31. Pyroformed is defined as any vapor deposited anisotropic pyrolytic graphite preformed shape which has been removed from the substrate upon which it was deposited. Pyrolytic graphite deposited on a base 26 such as coating 29 as shown in FIG. 4, can easily "be removed from the base as for example by positioning a collar around the substrate and pulling the substrate or base through the collar thus forcibly removing the deposition from the base. The electrode cup of FIG. 5 provides a high degree of uniformity over the entire surface and again short warm up times to peak arcing temperatures and uniform surface temperatures are achieved because of the circular nature of AB plane orientation.

FIGS. 6 and 7 depict boiler type electrode configurations with representative samples 32, 33 deposited on base members 34, 35 with isotropic counter electrodes 36, 37. In FIG. 6 a tip portion is formed from a cup similar to cup 30 depicted in FIG. 5. A central aperture 39 is bored in the tip thereof as shown. Any suitable cement may be used to bond the boiler tip 38 to the base 34. The advantages to be derived from this configuration utilizing pyroformed anisotropic pyrolytic graphite oriented as shown are as follows:

As in all boiler or furnace electrodes the sample volatilized in the furnace evolves through hole into are for excitation. 'Ihis separates the area of evolution and excitation and favors the more volatile elements such as mercury, cadmium, zinc, arsenic, etc., since the pyroformed furnace heats rapidly and uniformly to a relatively high temperature for furnace electrodes. Furthermore, an anisotropic substrate or base may advantageously be employed for the boiler electrodes of FIG. 6 to further concentrate the heat while still achieving uniformity of heat distribution.

In FIG. 7, the boiler tip 40 is machined from a block of pyrolytic graphite such that the AB planes are disposed normal to the central are axis and the C-axis is disposed parallel to the central arc axis. The advantages to be derived from this orientation are as follows. As in FIG. 6, the boiler electrode in this case has the combination of the hot and stable arc with a furnace that is thermally insulated by the C-axis of the pyrolytic graphite. Such electrodes favor the most volatile elements particularly mercury since the sample temperature is kept low and uniform volatilization results.

In FIG. 8, a pair of electrodes 41 having conventional base portions 42, 43 of graphite or the like are shown. Center post 44, specifically the AB edges surrounding the post on base 43 draws the arc. Stability and uniformity as well as rapid warm up time to peak operating arc temperature are enhanced by anisotropic coatings 45, 46. As shown, the coating on the top surface 47 of the post 44 is removed. This provides a AB edge or C-axis facing border 48 around the tip. Due to the circular orientation of the A-B planes surrounding the tip, the resulting uniform temperature distribution will aid in maintenance of a stable arc. Furthermore, the arc will strike the A-B edge and thus concentrate in the center post and be precluded from wandering to the sides of the cup because of the low thermal and electrical conductivity of the C-axis. The remaining surfaces of the cup being formed from A-B planes have all of the advantages discussed previously in connection with FIG. 4. The chart on FIG. 9 shows a comparison of spectral sensitivities using dimensionally equivalent electrodes conforming to FIGS. 1-3 and having the dimensional parameters indicated in FIG. 1 for a few specimen elements using Li Co as a matrix and .015 by weight sample specimens of Co, Y and Pb. Examination of the line background readings (dimensionless ratio of intensities) for the three samples vs. wavelength (angstroms) using a D.C. are running at 6 amp. for 30 sec. shows the order of improvement achieved with pyrolytic graphite having the A-B plane parallel to the arc axis;

FIG. 10 depicts a comparison of the electrodes depicted in FIGS. 1-3 with respect to the arcing characteristics of the individual electrodes as evidenced by the background radiation produced by each type. Percent transmission is a measure of the percent transmission of a white or non-coherent light source through film previously exposed to arcs produced by the electrodes depicted in FIGS. 1-3 for certain representative wavelengths. The higher the value of percent transmission the less background intensity emanating from the arc at, the particular wavelength under consideration. It is to be noted from FIG. 10 that background intensity is considerably reduced for A-B plane orientations thus providing excellent spectral sensitivities.

In any event the A-B plane or C-axis orientations will result in enhanced consistency of the background radiation emanating from the arc and thus considerably enhance the validity of plural analysis of a given sample to provide a high degree of accuracy heretofore unattainable in emission spectroscopic analysis. It is to be understood that the counter electrode shapes depicted in FIGS. 1-8 are merely illustrative and are not to be taken as being the only shape utilized for the particular sample electrode involved.

Other applications wherein a stable illumination source is required are search lights, motion picture projectors, illuminators for metallagraphs and are image furnaces. Anisotropic pyrolytic graphite electrodes such as shown and described herein are advantageously utilized in such applications. In particular, where the C-axis or low thermal and electrical conductivity axis is disposed parallel (aligned with) the axis of the arc, increased source stability is achieved.

Since many changes could be made in the "above con struction and many apparently widely diiferent embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. For use in an apparatus for the production of an intense are between a pair of electrodes disposed in spaced relation with respect to each other such that an arc is drawn between mutually opposed tip portions of said pair of electrodes for the spectroscopic analysis of a sample of material, an emission spectroscopic electrode having a tip portion which has a substantial portion thereof composed of anisotropic pyrolytic graphite, said anistropic pyrolytic graphite being characterized by having A-B planes and a C-axis wherein said A-B planes exhibit high thermal and electrical conductivity relative to the thermal and electrical conductivity of said C-axis, said AB planes of the pyrolytic graphite tip portion of said electrode being dis- 6 posed normal to the central axis of said emission spectroscopic electrode.

2. For use in an apparatus for the production of an intense are between a pair of electrodes disposed in spaced relation with respect to each other such that an arc is drawn between mutually opposed tip portions of said pair of electrodes for the spectroscopic analysis of a sample of material, an emission spectroscopic electrode having a tip portion which has a substantial portion thereof composed of anisotropic pyrolytic graphite, said anisotropic pyrolytic graphite being characterized by having A-B planes and a C-axis wherein said A-B planes exhibit high thermal and electrical conductivity relative .to the thermal and electrical conductivity of said C-axis, said A-B planes of the pyrolytic graphite tip portion of said electrode being disposed parallel to the central axis of said emission spectroscopic electrode.

3. For use in an apparatus for the production of an intense arc between a pair of electrodes disposed in spaced relation with respect to each other such that an arc is drawn between mutually opposed tip portions of said pair of electrodes for the spectroscopic analysis of a sample of material, an emission spectroscopic electrode having a tip portion which has a substantial portion thereof composed of anisotropic pyrolytic graphite, said anisotropic pyrolytic graphite being characterized by having A-B planes and a C-axis wherein said AB planes exhibit high thermal and electrical conductivity relative to the thermal and electrical conductivity of said C-axis, said A-B planes of the pyrolytic graphite tip portion of said electrode being disposed normal to the central axis of said emission spectroscopic electrode, said emission spectroscopic electrode having a base portion made of isotropic materials and said tip portion being an anisotropic pyrolytic graphite coating deposited on said base portion.

4. For use in an apparatus for the production of an intense arc between a pair of electrodes disposed in spaced relation with respect to each other such that an arc is drawn between mutually opposed tip portions of said pair of electrodes for the spectroscopic analysis of a sample of material, a first emission spectroscopic electrode having a tip portion which has a substantial portion thereof composed on anisotropic pyrolytic graphite, said anisotropic pyrolytic graphite being characterized by having A B planes and a C-axis wherein said A-B planes exhibit high thermal and electrical conductivity relative to the thermal and electrical conductivity of said C-axis, said A-B planes of the pyrolytic graphite tip portion of said electrode being disposed parallel to the central axis of said emission spectroscopic electrode, said emission spectroscopic electrode having a base portion made of isotropic material, said tip portion being an anisotropic pyrolytic graphite coating deposited on said base portion, the other electrode of said pair of electrodes being disposed along a common axis and having a tip portion made of anisotropic pyrolytic graphite.

5. For use in an apparatus for the production of an intense are between a pair of electrodes disposed in spaced relation with respect to each other such that an arc is drawn between mutually opposed tip portions of said pair of electrodes for the spectroscopic analysis of a sample of material, an emission spectroscopic electrode having a tip portion which has a substantial portion thereof composed of anisotropic pyrolytic graphite, said anisotropic pyrolytic graphite being characterized by having A-B planes and a C-axis wherein said A-B planes exhibit high thermal and electrical conductivity relative to the thermal and electrical conductivity of said C-axis, said electrode being disposed in combination with a mutually opposed counter electrode, each of said pair of electrodes including a base portion made of isotropic carbon and each of said tip portions being coatings of pyrolytic graphite deposited on said base portions, the A-B planes of the pyrolytic graphite tip portion of said one electrode being disposed parallel to the central axis of said one emission spectroscopic electrode and the A-B plane of the pyrolytic graphite tip portion of the other electrode of said pair of electrodes being disposed perpendicular to the central axis of said other emission spectroscopic electrode.

6. For use in an apparatus for the production of an intense are between a pair of electrodes disposed in spaced relation with respect to each other such that an arc is drawn between mutually opposed tip portions of said pair of electrodes for the spectroscopic analysis of a sample of material, an emission spectroscopic electrode having a tip portion which has a substantial portion thereof composed of anisotropic pyrolytic graphite, said anisotropic pyrolytic graphite being characterized by having A-B planes and a C-axis wherein said A-B planes exhibit high thermal and electrical conductivity relative to the thermal and electrical conductivity of said C-axis, said tip portion defining an open cup of pyroforrned pyrolytic graphite.

7. For use in an apparatus for the production of an intense arc between a pair of electrodes disposed in spaced relation with respect to each other such that an arc is drawn between mutually opposed tip portions of said pair of electrodes for the spectroscopic analysis of a sample of material, an emission spectroscopic electrode having a tip portion which has a substantial portion thereof composed of anisotropic pyrolytic graphite, said anisotropic pyrolytic graphite being characterized by having AB planes and a C-axis wherein said AB planes exhibit high thermal and electrical conductivity relative to the thermal and electrical conductivity ofsaid C-axis, said tip portion of said emission spectroscopic electrode defining at least a portion of an enclosed cavity having its cover portion formed from pyrolytic graphite, said,

cavity forming a boiler for volatization of a sample of material said boiler having an aperture in the cover portion thereof at the central axis of the electrode.

8. For use in an apparaus for the production of an intense are between a pair of electrodes disposed in spaced relation with respect to each other such than an arc is drawn between mutually opposed tip portions of said pair of electrodes for the spectroscopic analysis of a sample of material, an emission spectroscopic electrode having a tip portion which has a substantial portion thereof composed of anisotropic pyrolytic graphite, said anisotropic pyrolytic graphite being characterized by having A-B planes and a C-axis wherein said A-B planes exhibit high thermal and electrical conductivity relative to the thermal and electrical conductivity of said C-axis, said tip portion of said emission spectroscopic electrode defining at least a portion of an enclosed cavity having its cover portion formed from pyrolytic graphite, said cavity forming a boiler for volatization of a sample of material, said boiler having an aperture in the cover portion thereof at the central axis of the electrode, said' boiler cover portion having the AB planes of said pyrolytic graphite disposed normal to the central axis of said electrode.

9. For use in an apparatus for the production of an intense arm between a pair of electrodes disposed in spaced relation with respect to each other such that an arc is drawn between mutually opposed tip portions of said pair of electrodes for the spectroscopic analysis of a sample of material, an emission spectroscopic electrode having a tip portion which has a substantial portion thereof composed of anisotropic pyrolytic graphite, said anisotropic pyrolytic graphite being characterized by having A-B planes and a C-axis wherein said AB planes exhibit high thermal and electrical conductivity relative to the thermal and electrical conductivity of said C-axis, said tip portion of said emission spectroscopic electrode, defining at least a portion of an enclosed cavity having its cover portion formed from pyrolytic graphite, said cavity forming a boiler for volatization of a sample of material, said boiler having an aperture in the cover portion thereof at the central axis of the electrode, said boiler cover portion having the A-B planes of said pyrolytic graphite disposed parallel to the external defining surface thereof.

10. For use in an apparatus for the production of an intense are between a pair of electrodes disposed in spaced relation with respect to each other such that an arc is drawn between mutually opposed tip portions of said pair of electrodes for the spectroscopic analysis of a sample material, an emission spectroscopic electrode having a tip portion which has a substantial portion thereof composed of anisotropic pyrolytic graphite, said anisotropic pyrolytic graphite being characterized by having A-B planes and a C-axis wherein said A-B planes exhibit high thermal and electrical conductivity relative to the thermal and electrical conductivity of said C-axis, said tip portion of said emission spectroscopic electrode forming a cup having a central post therein,said tip portion and the sides of said central post having a coating of pyrolytic graphite deposited thereon.

11. For use in an apparatus for the production of an intense are between a pair of electrodes disposed in spaced relation with respect to each other such that an arc is drawn between mutually opposed tip portions of said pair of electrodes for the spectroscopic analysis of a sample of material, an emission spectroscopic electrode having a tip portion which has a substantial portion thereof composed of anisotropic pyrolytic graphite, said anisotropic pyrolytic graphite being characterized by having AB planes and a C-axis wherein said A-B planes exhibit high thermal and electrical conductivity relative to the thermal and electrical conductivity of said C-axis, said tip portion of said emission spectroscopic electrode forming a cup having an open cavity for receiving a sample of material for volatization, the surfaces of said cup being characterized by having the A-B planes of said pyrolytic graphite disposed parallel thereto.

12. In an apparatus for the spectroscopic analysis of a sample of material, a lower electrode having a cavity in its top portion for containing said sample of material, and an upper electrode spaced from the lower electrode, said upper electrode having a cylindrical body with a tapered lower end portion, said lower electrode having its cavity surface composed of anisotropic pyrolytic graphite, said anisotropic pyrolytic graphite being characterized by having A-B planes and a C-axis wherein said A-B planes exhibit high thermal and electrical conductivity relative to the thermal and electrical conductivity of said C-axis.

13. In an apparatus for the spectroscopic analysis of a sample of material, a lower electrode having a cavity in its top portion for containing said sample of material, and an upper electrode spaced from the lower electrode,

' said upper electrode having a cylindrical body with a tapered lower end portion, said lower electrode having its cavity surface composed of anisotropic pyrolytic graphite, said anisotropic pyrolytic graphite being characterized by having A-B planes and a C-axis wherein said AB planes exhibit high thermal and electrical conductivity relative to the thermal and electrical conductivity of said C-axis, said upper electrode having its tapered lower end portion composed of anisotropic pyrolytic graphite.

14. An electrode for producing an intense light by an arc discharge between at least a pair of electrodes, said electrode being characterized by having its tip portion formed from a hollow generally cone shaped deposit of anisotropic pyrolytic graphite, said anisotropic pyrolytic graphite being characterized by having A-B planes and a C-axis wherein said A-B planes exhibit high thermal and electrical conductivity relative to the thermal and electrical conductivity of said C-axis, said hollow generally cone shaped deposit of anisotropic pyrolytic graphite being deposited on the tip portion of an elongated rod of isotropic graphite.

15. A generally elongated rod shaped electrode for producing an intense light by an arc discharge between at least a pair of electrodes, said electrode being characterized by having its tip portion forming a cavity for receiving a sample of material, said cavity having its internal surface composed of anistropic pyrolytic graphite, said anisotropic pyrolytic graphite being characterized by having A-B planes and a C-axis wherein said A-B planes exhibit high thermal and electrical conductivity relative to the thermal and electrical conductivity of said C-axis, the A-B planes of said anisotropic pyrolytic graphite being disposed parallel to the internal surface of said cavity.

16. A generally elongated rod shaped electrode for producing an intense light by an arc discharge between at least a pair of electrodes, said electrode being characterized by having its tip portion forming a cavity for receiving a sample of material; said cavity having its internal surface composed of anisotropic pyrolytic graphite, said anisotropic pyrolytic graphite being characterized by having A-B planes and a C-axis wherein said A-B planes exhibit high thermal and electrical con ductivity relative to the thermal and electrical conductivity of saidC-axis, the A-B planes of said anisotropic pyrolytic graphite being disposed normal to the central axis of said rod shaped electrode.

17. A generally elongated rod shaped electrode for producing an intense light by an arc discharge between at least a pair of electrodes, said electrode being characterized by having its tip portion forming a cavity for receiving a sample of material, said cavity having its internal surface composed of anisotropic pyrolytic graphite, said anisotropic pyrolytic graphite being characterized by having AB planes and a C-axis wherein said A-B planes exhibit high thermal and electrical conductivity relative to the thermal and electrical conductivity of said C-axis,

said A-B planes of said anisotropic pyrolytic graphite being disposed parallel to the central axis of said rod shaped electrode.

18. A generally elongated rod shaped electrode for 4 producing an intense light by an arc discharge between at least a pair of electrodes, said electrode having its tip portion composed of anisotropic pyrolytic graphite deposited on the end portion of a rod of isotropic graphite, said anistropic pyrlytic graphite being characterized by having A-B planes and a C-axis wherein said A-B planes exhibit high thermal and electrical conductivity relative to the thermal and electrical conductivity of said C-axis, said anisotropic pyrolytic graphite forming said tip portion having its C-axis disposed parallel with respect to the central axis of said rod.

19. A generally elongated rod shaped electrode for producing an intense light by an arc discharge between at least a pair of electrodes, said electrode having its tip portion composed of anisotropic pyrolytic graphite deposited on the end portion of a rod of isotropic graphite, said anisotropic pyrolytic graphite being characterized by having A-B planes and a C-axis wherein said AB planes exhibit high thermal and electrical conductivity relative to the thermal and electrical conductivity of said C-axis, said anisotropic pyrolytic graphite forming said tip portion being a coating of anisotropic pyrolytic graphite having its A-B planes disposed parallel to the tip surfaces.

References Cited by the Examiner UNITED STATES PATENTS 1,019,463 3/ 1912 Hansen 23209.2 1,084,129 1/1914 Brown 2'3209.3 X 1,115,480 11/1914 Ayrton 313354 2,252,508 8/1941 Hoff 313357 2,303,514 12/1942 Toepfer 313-352 2,3 88,090 10/ 1945 Scott 313-352 X 2,599,179 6/1952 Hopkins v 313-355 X 3,131,290 4/1964 Stepath 313355 X 3,138,434 6/ 1964 Diefendorf 23-209.3

FOREIGN PATENTS 918,880 2/ 1963 Great Britain.

JOHN W. HUCKERT, Primary Examiner. JAMES KALLAM, Examiner.

DAVID J. GALVIN, A. I. JAMES, Assistant Examiners. 

1. FOR USE IN AN APPARATUS FOR THE PRODUCTION OF AN INTENSE ARC BETWEEN A PAIR OF ELECTRODES DISPOSED IN SPACED RELATION WITH RESPECT TO EACH OTHER SUCH THAT AN ARC IS DRAWN BETWEEN MUTUALLY OPPOSED TIP PORTIONS OF SAID PAIR OF ELECTRODES FOR THE SPECTROSCOPIC ANALYSIS OF A SAMPLE OF MATERIAL, AN EMISSION SPECTROSCOPIC ELECTRODE HAVING A TIP PORTION WHICH HAS A SUBSTANTIAL PORTION THEREOF COMPOSED OF ANISOTROPIC PYROLYTIC GRAPHITE, SAID ANISTROPIC PYROLYTIC GRAPHITE BEING CHARACTERIZED BY HAVING A-B PLANES AND A C-AXIS WHEREIN SAID A-B PLANES EXHIBIT HIGH THERMAL AND ELECTRICAL CONDUCTIVITY RELATIVE TO THE THERMAL AND ELECTRICAL CONDUCTIVITY OF SAID C-AXIS, SAID A-B PLANES OF THE PYROLYTIC GRAPHITE TIP PORTION OF SAID ELECTRODE BEING DISPOSED NORMAL TO THE CENTRAL AXIS OF SAID EMISSION SPECTROSCOPIC ELECTRODE. 